The usual commercial method for the manufacture of aminoformaldehyde resins such as urea-formaldehyde or melamine-formaldehyde resins is to react the amino compound and formaldehyde in an aqueous system at a temperature of 60.degree. to 90.degree. C.
The product in such cases will inevitably contain a large amount of water which for many uses has to be removed.
Thus the manufacture of moulding powders from such resins requires a lengthy process in which a large volume of water has to be removed.
We have also found that in the production of foam from urea-formaldehyde resin, as used, for example, for insulation purposes, foams of superior resilience may be produced from resins of low water content as described in our U.K. Patent Application No. 51269/77.
It has been disclosed (U.S. Pat. No. 1,985,937) that polyhydric alcohols can be reacted with methylol ureas, methyl esters thereof, or dimethyl thiourea to give a clear viscous solution.
It has been disclosed (U.S. Pat. No. 1,986,067) that urea can be reacted with a glycol and the product condensed with formaldehyde to give a resinous product.
Finally it has been disclosed (U.K. Pat. No. 1,107,245) that a polyetherurea can be obtained by reacting formaldehyde with glycol to produce a hemiformal, and then reacting the hemiformal with urea or thiourea.
However, in each of these three prior art disclosures the end product is a material containing a high proportion of glycol which has totally unsatisfactory properties when considered as replacement for modern urea-formaldehyde or melamine-formaldehyde resins.
It has been proposed (U.K. Pat. No. 1,390,370) to make amino-formaldehyde resins by reaction, in the absence of solvent, of urea or thiourea, paraformaldehyde, and hexamethylene tetramine in a molar ratio in the range from 1:1.1:0.01 to 1:25:0.2. This proposal, however, suffers from the difficulty that in the solid phase, reaction control is virtually impossible and a consistently satisfactory end product is not obtained.
The present invention is thus concerned with the problem of providing a process for the preparation of amino-formaldehyde resins of lower water content than by the conventional aqueous system, yet avoiding the difficulties of solid phase reaction.
We propose a solution to this problem in the specification of our co-pending U.K. Patent Application No. 21751/77 in which we describe a method for the manufacture of an amino-formaldehyde resin which comprises reacting an amino compound with formaldehyde or paraformaldehyde at a temperature above 60.degree. C. in the liquid phase, the liquid phase being ensured by the presence of a minor proportion of a reactive modifier being a compound capable of taking part in said reaction and also capable of modifying the mixture of reactants to be liquid at the temperature at which the reaction is to be carried out. Examples are given in that specification of the production of low-water content resins using various different compounds as reactive modifiers. The products so made are useful resins, but the reactive modifiers described are compounds which not only modify the reaction system to the liquid phase at the reaction temperature, but also modify the properties of the resulting resin from those of a simple urea-or melamine-formaldehyde resin.
The present invention has as its primary objective the preparation of amino-formaldehyde resin of lower water content than those obtained by the conventional aqueous system, whilst avoiding the need to use compounds which will modify the properties of the resin produced.